Ruby on Rails 3.2 Release Notes

Highlights in Rails 3.2:

Faster Development Mode
New Routing Engine
Automatic Query Explains
Tagged Logging

These release notes cover only the major changes. To learn about various bug fixes and changes, please refer to the changelogs or check out the list of commits in the main Rails repository on GitHub.

1. Upgrading to Rails 3.2

If you're upgrading an existing application, it's a great idea to have good test coverage before going in. You should also first upgrade to Rails 3.1 in case you haven't and make sure your application still runs as expected before attempting an update to Rails 3.2. Then take heed of the following changes:

1.1. Rails 3.2 requires at least Ruby 1.8.7

Rails 3.2 requires Ruby 1.8.7 or higher. Support for all of the previous Ruby versions has been dropped officially and you should upgrade as early as possible. Rails 3.2 is also compatible with Ruby 1.9.2.

Note that Ruby 1.8.7 p248 and p249 have marshalling bugs that crash Rails. Ruby Enterprise Edition has these fixed since the release of 1.8.7-2010.02. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults, so if you want to use 1.9.x, jump on to 1.9.2 or 1.9.3 for smooth sailing.

1.2. What to update in your apps

Update your Gemfile to depend on
- rails = 3.2.0
- sass-rails ~> 3.2.3
- coffee-rails ~> 3.2.1
- uglifier >= 1.0.3
Rails 3.2 deprecates vendor/plugins and Rails 4.0 will remove them completely. You can start replacing these plugins by extracting them as gems and adding them in your Gemfile. If you choose not to make them gems, you can move them into, say, lib/my_plugin/* and add an appropriate initializer in config/initializers/my_plugin.rb.

There are a couple of new configuration changes you'd want to add in config/environments/development.rb:

# Raise exception on mass assignment protection for Active Record models
config.active_record.mass_assignment_sanitizer = :strict

# Log the query plan for queries taking more than this (works
# with SQLite, MySQL, and PostgreSQL)
config.active_record.auto_explain_threshold_in_seconds = 0.5

The mass_assignment_sanitizer config also needs to be added in config/environments/test.rb:

# Raise exception on mass assignment protection for Active Record models
config.active_record.mass_assignment_sanitizer = :strict

1.3. What to update in your engines

Replace the code beneath the comment in script/rails with the following content:

ENGINE_ROOT = File.expand_path('../..', __FILE__)
ENGINE_PATH = File.expand_path('../../lib/your_engine_name/engine', __FILE__)

require "rails/all"
require "rails/engine/commands"

2. Creating a Rails 3.2 application

# You should have the 'rails' RubyGem installed
$ rails new myapp
$ cd myapp

2.1. Vendoring Gems

Rails now uses a Gemfile in the application root to determine the gems you require for your application to start. This Gemfile is processed by the Bundler gem, which then installs all your dependencies. It can even install all the dependencies locally to your application so that it doesn't depend on the system gems.

More information: Bundler homepage

2.2. Living on the Edge

Bundler and Gemfile makes freezing your Rails application easy as pie with the new dedicated bundle command. If you want to bundle straight from the Git repository, you can pass the --edge flag:

$ rails new myapp --edge

If you have a local checkout of the Rails repository and want to generate an application using that, you can pass the --dev flag:

$ ruby /path/to/rails/railties/bin/rails new myapp --dev

3. Major Features

3.1. Faster Development Mode & Routing

Rails 3.2 comes with a development mode that's noticeably faster. Inspired by Active Reload, Rails reloads classes only when files actually change. The performance gains are dramatic on a larger application. Route recognition also got a bunch faster thanks to the new Journey engine.

3.2. Automatic Query Explains

Rails 3.2 comes with a nice feature that explains queries generated by Arel by defining an explain method in ActiveRecord::Relation. For example, you can run something like puts Person.active.limit(5).explain and the query Arel produces is explained. This allows to check for the proper indexes and further optimizations.

Queries that take more than half a second to run are automatically explained in the development mode. This threshold, of course, can be changed.

3.3. Tagged Logging

When running a multi-user, multi-account application, it's a great help to be able to filter the log by who did what. TaggedLogging in Active Support helps in doing exactly that by stamping log lines with subdomains, request ids, and anything else to aid debugging such applications.

4. Documentation

From Rails 3.2, the Rails guides are available for the Kindle and free Kindle Reading Apps for the iPad, iPhone, Mac, Android, etc.

5. Railties

Speed up development by only reloading classes if dependencies files changed. This can be turned off by setting config.reload_classes_only_on_change to false.
New applications get a flag config.active_record.auto_explain_threshold_in_seconds in the environments configuration files. With a value of 0.5 in development.rb and commented out in production.rb. No mention in test.rb.
Added config.exceptions_app to set the exceptions application invoked by the ShowException middleware when an exception happens. Defaults to ActionDispatch::PublicExceptions.new(Rails.public_path).
Added a DebugExceptions middleware which contains features extracted from ShowExceptions middleware.
Display mounted engines' routes in rake routes.
Allow to change the loading order of railties with config.railties_order like:
```
config.railties_order = [Blog::Engine, :main_app, :all]
```
Scaffold returns 204 No Content for API requests without content. This makes scaffold work with jQuery out of the box.
Update Rails::Rack::Logger middleware to apply any tags set in config.log_tags to ActiveSupport::TaggedLogging. This makes it easy to tag log lines with debug information like subdomain and request id -- both very helpful in debugging multi-user production applications.
Default options to rails new can be set in ~/.railsrc. You can specify extra command-line arguments to be used every time rails new runs in the .railsrc configuration file in your home directory.
Add an alias d for destroy. This works for engines too.
Attributes on scaffold and model generators default to string. This allows the following: bin/rails g scaffold Post title body:text author
Allow scaffold/model/migration generators to accept "index" and "uniq" modifiers. For example,
```
$ bin/rails g scaffold Post title:string:index author:uniq price:decimal{7,2}
```
will create indexes for title and author with the latter being a unique index. Some types such as decimal accept custom options. In the example, price will be a decimal column with precision and scale set to 7 and 2 respectively.
Turn gem has been removed from default Gemfile.
Remove old plugin generator rails generate plugin in favor of rails plugin new command.
Remove old config.paths.app.controller API in favor of config.paths["app/controller"].

5.1. Deprecations

Rails::Plugin is deprecated and will be removed in Rails 4.0. Instead of adding plugins to vendor/plugins use gems or bundler with path or git dependencies.

6. Action Mailer

Upgraded mail version to 2.4.0.
Removed the old Action Mailer API which was deprecated since Rails 3.0.

7. Action Pack

7.1. Action Controller

Make ActiveSupport::Benchmarkable a default module for ActionController::Base, so the #benchmark method is once again available in the controller context like it used to be.
Added :gzip option to caches_page. The default option can be configured globally using page_cache_compression.
Rails will now use your default layout (such as "layouts/application") when you specify a layout with :only and :except condition, and those conditions fail.
```
class CarsController
  layout 'single_car', :only => :show
end
```
Rails will use layouts/single_car when a request comes in :show action, and use layouts/application (or layouts/cars, if exists) when a request comes in for any other actions.
form_for is changed to use #{action}_#{as} as the CSS class and id if :as option is provided. Earlier versions used #{as}_#{action}.
ActionController::ParamsWrapper on Active Record models now only wrap attr_accessible attributes if they were set. If not, only the attributes returned by the class method attribute_names will be wrapped. This fixes the wrapping of nested attributes by adding them to attr_accessible.
Log "Filter chain halted as CALLBACKNAME rendered or redirected" every time a before callback halts.
ActionDispatch::ShowExceptions is refactored. The controller is responsible for choosing to show exceptions. It's possible to override show_detailed_exceptions? in controllers to specify which requests should provide debugging information on errors.
Responders now return 204 No Content for API requests without a response body (as in the new scaffold).
ActionController::TestCase cookies is refactored. Assigning cookies for test cases should now use cookies[]
```
cookies[:email] = 'user@example.com'
get :index
assert_equal 'user@example.com', cookies[:email]
```
To clear the cookies, use clear.
```
cookies.clear
get :index
assert_nil cookies[:email]
```
We now no longer write out HTTP_COOKIE and the cookie jar is persistent between requests so if you need to manipulate the environment for your test you need to do it before the cookie jar is created.
send_file now guesses the MIME type from the file extension if :type is not provided.
MIME type entries for PDF, ZIP and other formats were added.
Allow fresh_when/stale? to take a record instead of an options hash.
Changed log level of warning for missing CSRF token from :debug to :warn.
Assets should use the request protocol by default or default to relative if no request is available.

7.1.1. Deprecations

Deprecated implied layout lookup in controllers whose parent had an explicit layout set:
```
class ApplicationController
  layout "application"
end

class PostsController < ApplicationController
end
```
In the example above, PostsController will no longer automatically look up for a posts layout. If you need this functionality you could either remove layout "application" from ApplicationController or explicitly set it to nil in PostsController.
Deprecated ActionController::UnknownAction in favor of AbstractController::ActionNotFound.
Deprecated ActionController::DoubleRenderError in favor of AbstractController::DoubleRenderError.
Deprecated method_missing in favor of action_missing for missing actions.
Deprecated ActionController#rescue_action, ActionController#initialize_template_class and ActionController#assign_shortcuts.

7.2. Action Dispatch

Add config.action_dispatch.default_charset to configure default charset for ActionDispatch::Response.
Added ActionDispatch::RequestId middleware that'll make a unique X-Request-Id header available to the response and enables the ActionDispatch::Request#uuid method. This makes it easy to trace requests from end-to-end in the stack and to identify individual requests in mixed logs like Syslog.
The ShowExceptions middleware now accepts an exceptions application that is responsible to render an exception when the application fails. The application is invoked with a copy of the exception in env["action_dispatch.exception"] and with the PATH_INFO rewritten to the status code.
Allow rescue responses to be configured through a railtie as in config.action_dispatch.rescue_responses.

7.2.1. Deprecations

Deprecated the ability to set a default charset at the controller level, use the new config.action_dispatch.default_charset instead.

7.3. Action View

Add button_tag support to ActionView::Helpers::FormBuilder. This support mimics the default behavior of submit_tag.
```
<%= form_for @post do |f| %>
  <%= f.button %>
<% end %>
```
Date helpers accept a new option :use_two_digit_numbers => true, that renders select boxes for months and days with a leading zero without changing the respective values. For example, this is useful for displaying ISO 8601-style dates such as '2011-08-01'.
You can provide a namespace for your form to ensure uniqueness of id attributes on form elements. The namespace attribute will be prefixed with underscore on the generated HTML id.
```
<%= form_for(@offer, :namespace => 'namespace') do |f| %>
  <%= f.label :version, 'Version' %>:
  <%= f.text_field :version %>
<% end %>
```
Limit the number of options for select_year to 1000. Pass :max_years_allowed option to set your own limit.
content_tag_for and div_for can now take a collection of records. It will also yield the record as the first argument if you set a receiving argument in your block. So instead of having to do this:
```
@items.each do |item|
  content_tag_for(:li, item) do
    Title: <%= item.title %>
  end
end
```
You can do this:
```
content_tag_for(:li, @items) do |item|
  Title: <%= item.title %>
end
```
Added font_path helper method that computes the path to a font asset in public/fonts.

7.3.1. Deprecations

Passing formats or handlers to render :template and friends like render :template => "foo.html.erb" is deprecated. Instead, you can provide :handlers and :formats directly as options: render :template => "foo", :formats => [:html, :js], :handlers => :erb.

7.4. Sprockets

Adds a configuration option config.assets.logger to control Sprockets logging. Set it to false to turn off logging and to nil to default to Rails.logger.

8. Active Record

Boolean columns with 'on' and 'ON' values are type cast to true.
When the timestamps method creates the created_at and updated_at columns, it makes them non-nullable by default.
Implemented ActiveRecord::Relation#explain.
Implements ActiveRecord::Base.silence_auto_explain which allows the user to selectively disable automatic EXPLAINs within a block.
Implements automatic EXPLAIN logging for slow queries. A new configuration parameter config.active_record.auto_explain_threshold_in_seconds determines what's to be considered a slow query. Setting that to nil disables this feature. Defaults are 0.5 in development mode, and nil in test and production modes. Rails 3.2 supports this feature in SQLite, MySQL (mysql2 adapter), and PostgreSQL.

Added ActiveRecord::Base.store for declaring simple single-column key/value stores.

class User < ActiveRecord::Base
  store :settings, accessors: [ :color, :homepage ]
end

u = User.new(color: 'black', homepage: '37signals.com')
u.color                          # Accessor stored attribute
u.settings[:country] = 'Denmark' # Any attribute, even if not specified with an accessor

Added ability to run migrations only for a given scope, which allows to run migrations only from one engine (for example to revert changes from an engine that need to be removed).
```
rake db:migrate SCOPE=blog
```
Migrations copied from engines are now scoped with engine's name, for example 01_create_posts.blog.rb.
Implemented ActiveRecord::Relation#pluck method that returns an array of column values directly from the underlying table. This also works with serialized attributes.
```
Client.where(:active => true).pluck(:id)
# SELECT id from clients where active = 1
```
Generated association methods are created within a separate module to allow overriding and composition. For a class named MyModel, the module is named MyModel::GeneratedFeatureMethods. It is included into the model class immediately after the generated_attributes_methods module defined in Active Model, so association methods override attribute methods of the same name.
Add ActiveRecord::Relation#uniq for generating unique queries.
```
Client.select('DISTINCT name')
```
..can be written as:
```
Client.select(:name).uniq
```
This also allows you to revert the uniqueness in a relation:
```
Client.select(:name).uniq.uniq(false)
```
Support index sort order in SQLite, MySQL and PostgreSQL adapters.
Allow the :class_name option for associations to take a symbol in addition to a string. This is to avoid confusing newbies, and to be consistent with the fact that other options like :foreign_key already allow a symbol or a string.
```
has_many :clients, :class_name => :Client # Note that the symbol need to be capitalized
```
In development mode, db:drop also drops the test database in order to be symmetric with db:create.
Case-insensitive uniqueness validation avoids calling LOWER in MySQL when the column already uses a case-insensitive collation.
Transactional fixtures enlist all active database connections. You can test models on different connections without disabling transactional fixtures.
Add first_or_create, first_or_create!, first_or_initialize methods to Active Record. This is a better approach over the old find_or_create_by dynamic methods because it's clearer which arguments are used to find the record and which are used to create it.
```
User.where(:first_name => "Scarlett").first_or_create!(:last_name => "Johansson")
```

Added a with_lock method to Active Record objects, which starts a transaction, locks the object (pessimistically) and yields to the block. The method takes one (optional) parameter and passes it to lock!.

This makes it possible to write the following:

class Order < ActiveRecord::Base
  def cancel!
    transaction do
      lock!
      # ... cancelling logic
    end
  end
end

as:

class Order < ActiveRecord::Base
  def cancel!
    with_lock do
      # ... cancelling logic
    end
  end
end

8.1. Deprecations

Automatic closure of connections in threads is deprecated. For example the following code is deprecated:
```
Thread.new { Post.find(1) }.join
```
It should be changed to close the database connection at the end of the thread:
```
Thread.new {
  Post.find(1)
  Post.connection.close
}.join
```
Only people who spawn threads in their application code need to worry about this change.
The set_table_name, set_inheritance_column, set_sequence_name, set_primary_key, set_locking_column methods are deprecated. Use an assignment method instead. For example, instead of set_table_name, use self.table_name=.
```
class Project < ActiveRecord::Base
  self.table_name = "project"
end
```
Or define your own self.table_name method:
```
class Post < ActiveRecord::Base
  def self.table_name
    "special_" + super
  end
end

Post.table_name # => "special_posts"
```

9. Active Model

Add ActiveModel::Errors#added? to check if a specific error has been added.
Add ability to define strict validations with strict => true that always raises exception when fails.
Provide mass_assignment_sanitizer as an easy API to replace the sanitizer behavior. Also support both :logger (default) and :strict sanitizer behavior.

9.1. Deprecations

Deprecated define_attr_method in ActiveModel::AttributeMethods because this only existed to support methods like set_table_name in Active Record, which are themselves being deprecated.
Deprecated Model.model_name.partial_path in favor of model.to_partial_path.

10. Active Resource

Redirect responses: 303 See Other and 307 Temporary Redirect now behave like 301 Moved Permanently and 302 Found.

11. Active Support

Added ActiveSupport:TaggedLogging that can wrap any standard Logger class to provide tagging capabilities.

Logger = ActiveSupport::TaggedLogging.new(Logger.new(STDOUT))

Logger.tagged("BCX") { Logger.info "Stuff" }
# Logs "[BCX] Stuff"

Logger.tagged("BCX", "Jason") { Logger.info "Stuff" }
# Logs "[BCX] [Jason] Stuff"

Logger.tagged("BCX") { Logger.tagged("Jason") { Logger.info "Stuff" } }
# Logs "[BCX] [Jason] Stuff"

The beginning_of_week method in Date, Time and DateTime accepts an optional argument representing the day in which the week is assumed to start.
ActiveSupport::Notifications.subscribed provides subscriptions to events while a block runs.
Defined new methods Module#qualified_const_defined?, Module#qualified_const_get and Module#qualified_const_set that are analogous to the corresponding methods in the standard API, but accept qualified constant names.
Added #deconstantize which complements #demodulize in inflections. This removes the rightmost segment in a qualified constant name.
Added safe_constantize that constantizes a string but returns nil instead of raising an exception if the constant (or part of it) does not exist.
ActiveSupport::OrderedHash is now marked as extractable when using Array#extract_options!.
Added Array#prepend as an alias for Array#unshift and Array#append as an alias for Array#<<.
The definition of a blank string for Ruby 1.9 has been extended to Unicode whitespace. Also, in Ruby 1.8 the ideographic space U`3000 is considered to be whitespace.
The inflector understands acronyms.
Added Time#all_day, Time#all_week, Time#all_quarter and Time#all_year as a way of generating ranges.
```
Event.where(:created_at => Time.now.all_week)
Event.where(:created_at => Time.now.all_day)
```
Added instance_accessor: false as an option to Class#cattr_accessor and friends.
ActiveSupport::OrderedHash now has different behavior for #each and #each_pair when given a block accepting its parameters with a splat.
Added ActiveSupport::Cache::NullStore for use in development and testing.
Removed ActiveSupport::SecureRandom in favor of SecureRandom from the standard library.

11.1. Deprecations

ActiveSupport::Base64 is deprecated in favor of ::Base64.
Deprecated ActiveSupport::Memoizable in favor of Ruby memoization pattern.
Module#synchronize is deprecated with no replacement. Please use monitor from ruby's standard library.
Deprecated ActiveSupport::MessageEncryptor#encrypt and ActiveSupport::MessageEncryptor#decrypt.
ActiveSupport::BufferedLogger#silence is deprecated. If you want to squelch logs for a certain block, change the log level for that block.
ActiveSupport::BufferedLogger#open_log is deprecated. This method should not have been public in the first place.
ActiveSupport::BufferedLogger's behavior of automatically creating the directory for your log file is deprecated. Please make sure to create the directory for your log file before instantiating.
ActiveSupport::BufferedLogger#auto_flushing is deprecated. Either set the sync level on the underlying file handle like this. Or tune your filesystem. The FS cache is now what controls flushing.
```
f = File.open('foo.log', 'w')
f.sync = true
ActiveSupport::BufferedLogger.new f
```
ActiveSupport::BufferedLogger#flush is deprecated. Set sync on your filehandle, or tune your filesystem.

12. Credits

See the full list of contributors to Rails for the many people who spent many hours making Rails, the stable and robust framework it is. Kudos to all of them.

Rails 3.2 Release Notes were compiled by Vijay Dev.